This invention relates to electric furnaces and has particular application in producing carbon-impregnated articles by the deposition of carbon from a gas within a body of open porosity.
A deposition process is known, e.g. as described in U.S. Pat. No. 3,164,487, in which a thermal gradient is established across the body of open porosity (the body being of relatively low thermal conductivity) such that the temperature in an initial zone of the body is raised to a temperature sufficient to deposit carbon from the gas and thereby impregnate the initial zone, the temperature of remainder of the body being too low to cause deposition. The temperature of the initial zone is then progressively raised to maintain an impregnated/non-impregnated boundary which advances through the body, the rate of rise of temperature being limited so that the zone defined by the advancing boundary is substantially fully impregnated. The gas is normally a hydrocarbon and the process is mainly applicable to the impregnation of porous carbon bodies, e.g. made of fine carbon particles, or of carbon fibres or fabrics.
The present invention provides a furnance suitable for carrying out the above process with increased economy. In one form the invention provides a furnace suitable for impregnating simultaneously a plurality of bodies, particularly flat bodies such as sheets, or discs for use in disc brake assemblies.